• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.6
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• pp.467-474
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• 2012

UAVs for reconnaissance and intelligence operations require long endurance capability, which demands high efficiency of the propulsion system. The distributed propulsion system(DPS) generates the thrust by replacing a large propulsion system with a number of small propulsion systems. A DPS distributed along the wing span can produce gains in propulsion efficiency by reducing ejection velocity. Also, the ingestion of boundary layers through the distributed DPS inlet and ejecting flow from the outlet can improve the lift to drag ratio of the vehicle. This study investigates the effects of locations and size of the inlet and outlet of the DPS on the blended-wing-body design based on Eppler 337 airfoil, with a CFD tool. The fans in the DPS are modeled as actuator disks for computational efficiency. The best location and aspect ratio of the inlet and outlet are found from lift-to-drag ratio and pitching moment considerations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.733-734
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• 2008

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.133-134
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• 2007

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.669-670
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• 2009

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.272-272
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• 2014

니켈-텅스텐 합금은 hydrogen evolution reaction의 electrocatalytic으로 이용가능하다. 니켈-텅스텐 합금 도금은 니켈에 비해 큰 텅스텐의 원자 부피에 의해 큰 internal stress를 갖는다. 니켈-텅스텐 합금과 낮은 adhesion을 갖는 물질에 도금을 하여 외부에서 stress를 가하면 큰 표면적을 갖는 니켈-텅스텐 편상 합금을 얻을 수 있다. 도금 시간 및 외부의 stress를 이용하여 다양한 크기의 니켈-텅스텐 편상 합금 분물을 얻을 수 있었다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.151-151
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• 2014

최근 Touch Screen, OLED, Display, 등과 같은 분야에서 투명전도체 재료를 이용한 연구가 활발히 진행되고 있다. 투명전도체의 재료 중 가장 대표적인 물질은 ITO(Indium tin oxide)가 있지만 ITO는 제한된 매장량과 가격 상승 등의 이유로 이를 대체하기 위한 재료 개발이 필요하다. 본 연구에서는 ITO를 대체할 수 있는 나노섬유전기방사 공정을 통해서 100nm 이하의 직경을 가진 고정횡비 Ni 나노섬유를 만들 수 있다.

• Polymer Science and Technology
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• v.22 no.3
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• pp.224-229
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• 2011

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.743-744
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• 2011

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.2
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• pp.10-16
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• 2003

The unsteady supersonic flow over tandem cavities has been analyzed by the integration of Navier-Stokes equations with the k-$\varepsilon$ turbulence model. The unsteady flow is characterized by the periodicity due to the mutual relation between the shear layer and the internal flow in cavities. The upwind TVD scheme based on the flux vector split with the van Leer limiters is used. The results show the principal frequency is very reasonable. The principal frequency of the rear cavity due to the front cavity has been analyzed by the combination of the several aspect ratios of cavities. In the case of the front cavity of low aspect ratio, the frequencies of tandem cavities are almost same, because two shear layers developed from each cavity are mixed and developed to one shear layer. However, in the case of the front cavity of high aspect ratio, the characteristis of frequency are very different, because the second shear layer is developed in the diffused first shear layer.

• Journal of the Korea Convergence Society
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• v.12 no.9
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• pp.153-159
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• 2021

In this study, basic data that can be referenced for ventilation modeling was presented by analyzing the characteristics of wind pressure coefficients(Cp) according to wind direction angles under conditions of different building layouts and aspect ratios through CFD (Computational Fluid Dynamics) analysis for flat-type apartment complexes. In the case of a wind direction angle of 0°, Cp distribution in the form of an inverted S-shape was shown on the front of the building located on the windward side. And Cp corresponding to the lowest floor, the uppermost floor, and the two inflection points showed relatively close values regardless of the height of the building. The inflection point of the low-rise part was formed at a height of about 11m, and the height of the high-rise part could be calculated through a trend formula proportional to the height of the building. It was confirmed that the averaged Cp value can be applied in most conditions except for the wind direction angle of 45 degrees.